Cutting Tool Materials Guide: HSS, Cobalt, Carbide, PCBN & PCD Explained

Cutting tools are manufactured from one of seven distinct material families, each suited to different applications and cost positions: HSS (high-speed steel — entry-level), HSS-Co (cobalt high-speed steel — better for harder materials), HSSE / PM-HSS (premium powdered-metallurgy HSS — best HSS toughness-and-wear balance), Solid Carbide (VHM) (tungsten carbide — 3-5× HSS performance, brittle), Cermet (ceramic-metal composite — finishing only), PCBN (polycrystalline cubic boron nitride — second-hardest material on earth, for hardened steel), and PCD (polycrystalline diamond — hardest cutting tool material, non-ferrous only). Each material has a specific role; matching the right tool material to the application is the single biggest factor in cutting tool economics.

This reference compiles data from ASM Handbook Volume 16 (Machining), Sandvik Coromant Cutting Tool Materials Handbook, Kennametal Material Science Reference, and ISO 513 (the K-grade carbide classification standard).

Cutting Tool Materials — Properties at a Glance

Hardness, temperature stability, toughness, and cost positioning across the seven material families. Cost index is multiples of standard HSS price for an equivalent tool size (e.g. a HSS-Co 8% tool is roughly 1.6× the price of an equivalent HSS tool; solid carbide 4-8× depending on grade and coating).

HSS vs HSS-Co vs PM-HSS — What's the Real Difference?

HSS (M2) — The Baseline

Standard tungsten-molybdenum high-speed steel. Hardness ~850 HV at room temperature, retains 200 HV at 600°C. Works fine on mild steel and lower-carbon steels up to about M30 / 200 HB at moderate cutting speeds (Vc 25-30 m/min). Inexpensive, regrindable, the default base for entry-tier drills, taps, endmills, and reamers.

HSS-Co (M35 / M42) — Add Cobalt for Heat Resistance

HSS-Co adds 5-8% cobalt to the alloy. The cobalt content sustains hardness at higher cutting temperatures — a 5% Co tool retains ~350 HV at 600°C (vs HSS at 200 HV), and 8% Co retains ~400 HV. This is the right choice for stainless steel (where the cutting zone heats rapidly due to work-hardening), alloy steels, and harder applications. Cost premium ~30-60% over standard HSS.

PM-HSS — Powdered Metallurgy Process Improvement

PM-HSS uses powder-metallurgy manufacturing — fine alloy powder is sintered under pressure rather than cast. The result: finer and more uniform grain structure than conventionally-cast HSS-Co at equivalent cobalt content. Practical consequence: the tool is sharper at the cutting edge (finer grain = smaller possible edge radius) AND tougher (uniform grain resists crack propagation). Cost premium 50-200% over standard HSS.

Cost ladder summary: HSS ($) → HSS-Co 5% ($$) → HSS-Co 8% ($$) → PM-HSS V3 ($$$) → PM-HSS Co ($$$$) → SPM ($$$$$).

Why Solid Carbide (VHM) Outperforms HSS by 3-5×

Tungsten carbide (specifically Vollhartmetall — VHM, solid carbide — typically K15-K30 grades with sub-micron grain structure) retains approximately 80% of its room-temperature hardness at 600°C. Standard HSS retains only 25% at that temperature. This single property — sustained hot hardness — is what enables carbide tooling to run at 5× the cutting speed of HSS:

• Higher cutting speed = higher metal removal rate = faster cycle time
• Lower wear rate at speed = longer tool life = lower cost per part machined
• Higher thermal stability = MQL or dry machining possible (carbide doesn't require flood coolant the way HSS does)

BUT — carbide is BRITTLE. Toughness (resistance to fracture) is significantly lower than HSS. Carbide will chip or fracture in interrupted cuts, unstable setups, or impact loading. The trade-off is real: in a production environment with rigid setups and continuous cuts, carbide is 5-10× more economical per part. In a workshop with intermittent cuts and variable setups, HSS-Co is often the right choice.

K-grade carbide classification (per ISO 513) ranges from K10 (hardest, most wear-resistant, lowest toughness) through K20 (general-purpose) to K30 (toughest, lower wear resistance). For machining cast iron and non-ferrous: K10-K15. For general steel cutting: K20. For interrupted cuts or unstable conditions: K25-K30.

When to Choose Cermet (Finishing Only)

Cermet (a contraction of "ceramic" + "metal") is a composite of TiC or TiN ceramic phases bonded with nickel or cobalt metal binder. It sits between conventional carbide and pure ceramic on the hardness/toughness curve — harder than carbide (1,500 HV vs 1,400) but more brittle.

Cermet's narrow application zone: high-speed finishing of steel and stainless at light depth of cut (typically 0.1-0.5mm). It outperforms carbide on surface finish quality and edge wear at light cuts. It cannot rough — the brittleness causes catastrophic failure under heavy load or interrupted cuts.

Practical workflow: use a carbide endmill for roughing operations, swap to a cermet endmill for finishing passes. Cermet is rarely used for drilling (the entry shock fractures it) or for tapping (the multi-edge engagement geometry compounds the brittleness risk).

PCBN — The "Almost Diamond" for Hardened Steel

PCBN (Polycrystalline Cubic Boron Nitride) is the second-hardest material on earth, after diamond. Hardness ~3,500 HV — 2.5× harder than solid carbide. The critical edge over diamond: PCBN does not chemically react with iron. (Diamond's carbon catalyses with iron at cutting temperatures, dissolving the tool tip.)

This combination makes PCBN the right tool for hardened steel applications above 55 HRC — the dominant application class is finish-turning bearing races, automotive crankshafts after heat treatment, die finishing, and other operations where the workpiece is harder than carbide would survive at production cutting speeds.

Cost positioning: PCBN insert costs are 15-30× carbide. Tool life can be 50-200× carbide on hardened steel. The economic crossover is around production-volume work — for one-off or low-volume hardened steel work, carbide TiAlN or AlCrN remains more economical.

PCBN is also used (less commonly) for high-speed roughing of grey cast iron and for super-alloy finishing operations.

PCD — Hardest Cutting Material, One Application Class

Polycrystalline Diamond (PCD) is the hardest cutting tool material commercially available — ~8,000-10,000 HV, more than 5× the hardness of solid carbide. PCD is manufactured by sintering synthetic diamond particles with a cobalt binder under extreme pressure and temperature, then brazing the resulting tip onto a carbide substrate.

PCD has one fatal limitation: at cutting temperatures above ~600°C, the carbon in the diamond catalytically reacts with iron, dissolving the tool tip. This makes PCD useless on ferrous metals. Use PCD only on:

• Aluminium at extreme speed — automotive engine block production, aerospace aluminium machining at Vc up to 1,500-3,000 m/min
• Composites — CFRP and GFRP drilling and trimming, where the abrasive carbon and glass fibres destroy any other tool material
• Graphite — EDM electrode machining, where the abrasive graphite dust wears carbide rapidly
• MMCs (Metal Matrix Composites) and ceramics
• Copper alloys at extreme speeds

Cost positioning: 20-40× carbide. Tool life in non-ferrous machining can be 100-500× carbide. Reserved for production-volume work where the cost is amortised across thousands of parts.

Cost vs Tool Life — The Right Math

The most common mistake in cutting tool selection is buying the lowest tool purchase price. The right question is cost per part machined, calculated as:

Cost per part = Tool purchase price ÷ Tool life (parts produced per tool)

Worked example — drilling 100,000 holes in mild steel with a 10mm drill:

• Standard HSS drill — purchase price ~A$20, expected life ~50 holes per tool = 2,000 tools required = ~A$40,000 total, A$0.40 per hole
• HSS-Co 5% — purchase price ~A$45, expected life ~300 holes = 333 tools = ~A$15,000 total, A$0.15 per hole
• Solid carbide TiAlN — purchase price ~A$180, expected life ~5,000 holes = 20 tools = ~A$3,600 total, A$0.036 per hole

The "expensive" carbide tool is 10× cheaper per part than the "cheap" HSS tool. The same maths drives the entire cutting tool industry — production environments standardise on solid carbide because the cost-per-part economics dominate at volume. Workshop environments use HSS or HSS-Co because tool-purchase capital is the constraint, not labour cost amortised across thousands of parts.

The honest exception: rigid setup is required for carbide. If your machine, workholding, or toolholding can't provide the rigidity carbide demands, the cost-per-part calculation goes backwards (carbide breaks, life collapses, HSS wins). Assess your setup before assuming carbide is automatically the right answer.

AIMS Cutting Tool Material Range

AIMS Industrial stocks the full tool material spectrum:

• HSS jobber drills — entry-tier general-purpose drills for mild steel and softer materials
• HSS-Co 5% drills — Sutton D108 (Metric and Imperial), Bordo 2010 / 2011 / Imperial series. The standard for stainless and alloy steel.
• HSS-Co 8% drills — Sutton D109 Heavy Duty Cobalt Jobber. The premium HSS tier for production work.
• PM-HSS taps — premium tapping range across Sutton and other brands. Verify specific PM-HSS series with AIMS sales.
• Solid carbide drills — Sutton D300 (uncoated), D304/D306/D310 (entry-tier coated), D323/D326/D329/D332/D335 (AlCrN premium), D356/D358 Black Magic (Helica premium). See cutting tool coatings guide for coating selection.
• Solid carbide micro drills — Seco SD22 / SD26 series
• Solid carbide endmills — Sutton + other brands, multiple flute and helix configurations
• PCBN and PCD inserts — special order through AIMS for production-volume hardened steel or non-ferrous machining. Contact AIMS for sourcing.

Browse the full Sutton Tools range (Australian-made HSS, cobalt, and solid carbide cutting tools), cobalt drill bits for the HSS-Co tier, or carbide drill bits for solid carbide.

Need help matching tool material to a specific application — particularly hardened steels, super alloys, or production-volume cost-per-part economics? Contact AIMS on (02) 9773 0122.

Frequently Asked Questions

Q: What's the difference between HSS and carbide drill bits?

HSS (high-speed steel) is a tough, heat-resistant alloy that machines mild and medium-hard materials at moderate speeds. Solid carbide (VHM) is a sintered tungsten-carbide composite that's 3-5× harder than HSS and retains 80% of its hardness at 600°C (HSS retains only 25%). Carbide cuts 3-5× faster than HSS but is brittle — needs rigid setup and continuous cut. For production volume, carbide is 5-10× more economical per part. For workshop work with variable conditions, HSS-Co remains the right choice.

Q: Is cobalt better than HSS?

Yes — for harder materials and higher heat applications. HSS-Co adds 5-8% cobalt to standard high-speed steel, which sustains hardness at higher cutting temperatures. A 5% Co tool retains ~350 HV at 600°C vs HSS at 200 HV. This makes HSS-Co the right choice for stainless steel (where the cutting zone heats rapidly due to work-hardening), alloy steel, and harder applications. Cost premium is 30-60% over standard HSS — worth it whenever the work is in stainless or harder material.

Q: What is PM-HSS made of?

PM-HSS (Powdered Metallurgy High-Speed Steel) is high-speed steel manufactured by sintering fine alloy powder under pressure rather than conventional casting. The result: finer and more uniform grain structure than cast HSS-Co at equivalent cobalt content. This makes PM-HSS tools sharper at the cutting edge (finer grain = smaller edge radius) AND tougher (uniform grain resists crack propagation). PM-HSS V3 has vanadium for added wear resistance; PM-HSS Co has 8-12% cobalt for thermal stability.

Q: When do I need a solid carbide drill instead of HSS?

Three criteria: production volume (carbide pays back at 1,000+ holes per tool), material hardness (above ~32 HRC, HSS softens too rapidly), or cutting speed requirement (above ~80 m/min on steel, HSS fails). For one-off jobs in mild steel, HSS-Co is cheaper. For drilling thousands of holes in production, carbide is 5-10× more economical per part. For hardened steel above 45 HRC, carbide is essentially mandatory.

Q: What's VHM in drill terminology?

VHM stands for 'Vollhartmetall' — German for 'solid hard metal' / solid carbide. The term originated in German engineering and is now used internationally for solid carbide cutting tools (as distinct from carbide-tipped tools where a carbide insert is brazed onto an HSS body). VHM tools are made entirely from sintered tungsten carbide with a cobalt binder — typically K15 to K30 grade with sub-micron grain structure.

Q: HSS-Co vs HSSE-Co — what's the difference?

Both have cobalt — the difference is the base steel alloy. HSS-Co adds cobalt to standard HSS (typically M2). HSSE-Co adds cobalt to HSSE — a vanadium-grade premium HSS. The HSSE base gives higher wear resistance; the cobalt gives thermal stability. HSSE-Co is the premium HSS tier — typically used for heavy-duty tapping in difficult materials and for premium drills/endmills where carbide isn't economically justified.

Q: Can I use a diamond drill bit on steel?

No — diamond catalytically reacts with iron at cutting temperatures, dissolving the tool tip rapidly. Diamond (PCD or CVD diamond) is only for non-ferrous materials: aluminium at extreme speed, copper alloys, composites (CFRP/GFRP), graphite, MMCs, and ceramics. For steel of any kind — carbon, alloy, stainless, hardened — use carbide with TiAlN or AlCrN coating, or PCBN for very hard steels (>55 HRC).

Q: What is PCBN used for?

PCBN (Polycrystalline Cubic Boron Nitride) is the second-hardest material on earth, after diamond. Critical edge: PCBN does NOT react with iron. This makes PCBN the right tool for hardened steel above 55 HRC — finishing bearing races, automotive crankshafts after heat treatment, finishing dies, and similar operations. PCBN is also used for high-speed grey cast iron machining and super-alloy finishing. Cost is 15-30× carbide, but tool life on hardened steel is 50-200× carbide — economic crossover at production volume.

Q: Cermet vs carbide — which one for finishing?

Cermet for finishing only, carbide for general use. Cermet (TiC/TiN ceramic-metal composite) is harder than carbide (~1,500 HV vs 1,400) and gives superior surface finish at light depth of cut, but is more brittle — cannot rough. Practical workflow: rough with a carbide endmill, finish with a cermet endmill. Cermet is rarely used for drilling (entry shock fractures it) or tapping (multi-edge engagement compounds brittleness).

Q: Why are carbide tools brittle?

Tungsten carbide is a ceramic — a hard, crystalline compound (WC) bonded with a small percentage of metallic cobalt (typically 6-12%). The cobalt provides some toughness but the bulk of the material is brittle ceramic. The trade-off is fundamental: hardness comes from the WC ceramic phase; toughness would require more metallic binder, which reduces hardness. K-grade classification (K10-K30 per ISO 513) lets you trade hardness for toughness within carbide grades. K10 = hardest, most brittle. K30 = toughest, less hard.

Q: How long does an HSS drill bit last vs a carbide drill bit?

Application-dependent, but typical ranges in mild steel at 10mm Ø: HSS drill = 30-100 holes per tool. HSS-Co = 150-500 holes. Solid carbide TiAlN = 3,000-10,000 holes. The order-of-magnitude difference is what drives production cutting tool economics. In harder materials (stainless, alloy steel, hardened steel) the gap widens — HSS-Co might last 50 holes in 304 stainless where carbide TiAlN does 2,000+.

Q: What's the K-grade system in carbide?

ISO 513 classifies carbide grades from K01 (hardest, lowest toughness, for highest-precision and finest finish) through K10, K20 to K40 (toughest, lowest hardness, for interrupted cuts and roughing). The number indicates the trade-off position. For practical use: K10-K15 for cast iron and non-ferrous; K20 for general steel cutting; K25-K30 for interrupted cuts or unstable setups; K40 for very tough applications. The full ISO 513 system also has P-grades (for steel), M-grades (for stainless), and S/H-grades (for super alloys / hardened materials) — though K-grades are the most commonly referenced.

Related AIMS Engineering Reference Guides

• Workpiece Material Cross-Reference Chart
• Cutting Speeds & Feeds Master Reference
• Cutting Tool Troubleshooting Master
• Cutting Tool Coatings Guide (TiN, TiAlN, AlCrN, TiCN)
• Carbide vs HSS End Mills — Detailed Comparison (sister article — when carbide pays back)
• Cobalt Drill Bit Guide (sister article — HSS-Co tier detail)
• Hardness Testing & Conversion Reference